#-*- coding:utf-8 -*-

# if __name__ == '__main__':
#     print "hello,world"

import copy

a = [[1],[2],[3]]
b = copy.deepcopy(a)

print "before", "=>"
print a
print b

# modify original
a[0][0] = 0
a[1] = None

print "after", "=>"
print a
print b



